1. Field of the Invention
The present invention relates to an endoscope automatic light control apparatus provided with an automatic light control means and an automatic gain control means, and relates to an endoscope apparatus making use of the same.
2. Related Art Statement
In recent years, endoscopes have been widely put into practical use which observe the internal organs in the body cavity by inserting an elongated insert section into the body cavity, and as occasion arises, are able to give various medical treatments by using instruments inserted into instrument channels.
Also, various electronic endoscopes have been proposed by using solid state imaging devices such as a charged coupled device(CCD) as an imaging means.
As an automatic light control means of the electronic endoscopes, there are electronic endoscopes wherein both an iris control means for controlling the quantity of illuminating light and an automatic gain control means for controlling its video signal output are used. For example, in the specification of Ser. No. 244,777, by means of establishing a switch for controlling the quantity of light of an operating panel, an electronic endoscope apparatus is proposed to expand the dynamic range and to realize a high-speed control with good response by changing the same quantity of the reference levels of an automatic light control means(ALC) and an automatic gain control means (AGC) to the same direction by using such an iris. Since endoscopes are used under a special condition that is a condition in the body cavity, special attention should be paid to a detecting circuit for detecting brightness information in the ALO and the AGC. For example, when a hollow portion such a the gullet is observed, it is desirable that a peak value detection for detecting a peak value of a signal as a controlling signal should be used. If an average value detection is used for detecting an average value of a signal as a controlling signal, a halation is apt to be generated and, according to circumstances, there is a case of being unable to control the quantity of light even if a switch for controlling the quantity of light is adjusted to the darkest. In contrast with this, in case forceps are used, because the ALC and the AGC respond to a part of forceps having a very high reflection factor unless an average detection is used, there is a defect that the part of observation becomes dark. For the reasons mentioned above, it is necessary for an electronic endoscope apparatus to change a peak value detecting circuit with an average detecting circuit as occasion arises.
In an automatic light control circuit by using both the ALC and the AGC, the ALC was able to change the peak value detection with the average value detection and the AGC was fixed on either the peak value detection or the average value detection so far.
According to such prior art, electronic endoscopes have the following defect when they are used. That is to say, in case the ALC uses the peak value detection and the AGC uses the average value detection, a detecting level of the AGC falls and the AGC operates in the direction of increasing the gain, because the ALC operates to adjust the brightness of a projection such as a polyp. As a result, the polyp becomes brighter than its adjustment. Also, because the gain of the AGC increases, a signal to noise ratio(S/N) becomes worse. In contrast with this, in case the ALC uses the average value detection and the AGC uses the peak value detection, there is a case where the peak value detecting circuit responds to a slight spot and it does not operate in the direction of increasing the gain and the observation scope becomes narrower, in spite of an opening of an iris's full width when the stomach walls are observed.